Obesity in the United States is highly prevalent, approaching 60% for black women. Our hypothesis was that nutrition education at the work place added to internet-based wellness information and exercise resources would facilitate weight and fat mass loss in a racially diverse population of overweight female employees. Methods: 199 (average body mass index 33.96.3 kg/m2) non-diabetic women (57% black) at our institution were randomized to a 6 month program of either internet-based wellness information (WI) combined with dietitian-led nutrition education group sessions (GS) weekly for 3 months and then monthly with shift in emphasis to weight loss maintenance (n=99) or to WI alone (n=100). All were given access to exercise rooms convenient to their work site. Fat mass was measured by dual-energy x-ray absorptiometry. Results: WI+GS subjects lost more weight than WI subjects at 3 months (-2.22.8 vs. -1.03.0 kg, P>0.001). Weight (-2.73.9 vs. -2.03.9 kg) and fat mass (-2.23.1 vs. -1.73.7 kg) loss at 6 months was significant for WI+GS and WI groups (both P<0.001), but without significant difference between groups (both P>0.10); 27 % of the WI+GS group achieved 5% loss of initial weight as did 18% of the WI group (P=0.180). Blacks and whites similarly completed the study (67% versus 74%, P=0.303), lost weight (-1.83.4 versus -3.35.2 kg, P=0.255) and fat mass (-1.62.7 versus -2.54.3 kg, P=0.532), and achieved 5% loss of initial weight (21% versus 32%, P=0.189), irrespective of group assignment. We conclude that overweight women provided with internet-based wellness information and exercise resources at the work site lost weight and fat mass, with similar achievement by black and white women. Sustained benefit of nutrition education sessions, apparent at 3 months, may require continuation of weekly meetings with emphasis on continued weight loss, especially for subjects who fail to achieve weight loss goals. Black women are disproportionately affected by obesity and type 2 diabetes. Interventions have generally produced little weight loss and change in insulin sensitivity in black women, but we considered whether emphasis on mean data may obscure metabolic benefits to some and possible harms of participation in others. Accordingly, we analyzed insulin sensitivity by tertile of changes in fat mass (FM) in black women at NIH participating in a 6 month weight loss program at our institution. Methods: Fifty-four black women age 4510 years (meanSD), BMI range 25.9 to 54.7 kg/m2 completed a 6-month program that included group sessions, internet-based nutrition information and access to exercise facilities at the work site. FM was measured by dual-energy X-ray absorptiometry and insulin sensitivity index (SI) was calculated from the minimal model. Exercise performance was measured by peak oxygen consumption during treadmill exercise. Results: Following completion of the 6 month program, the cohort as a whole lost modest FM (baseline 40.812.4 to 39.412.6 kg, P<0.01), but 17 women gained FM. SI on average did not change (baseline 3.301.71 to 3.211.56, p=0.67), however the tertile with greatest FM loss (-3.6 kg, range -10.7 to -1.7 kg) had increased SI (+0.31.2), whereas the tertile with net FM gain (+0.9 kg, range -0.1 to +3.8 kg) had reduced SI (-0.71.3, P<0.05 for trend). The tertile with greatest FM loss also had improved exercise performance (+2.62.9 mLO2/kg/min) vs. the tertile with net FM gain (-0.32.7 mLO2/kg/min, P<0.05 for trend), but only change in FM remained an independent predictor of change in SI by multivariable regression analysis.We conclude that black women who achieve FM loss may improve insulin sensitivity and exercise performance, but FM gain with opposite outcomes is common. Focusing on participants who fail to achieve FM loss early in an intervention may be required to achieve success.